A method for manufacturing melt materials of copper, chromium and at least one readily evaporable component has been described in H. Hassler et al. (Eur. Pat. No. 115,292). Materials manufactured in accordance with this method were first used as contact material for vacuum medium voltage power switches with switch-off current above 10 kA. R. Mueller et al. (Eur. Pat. No. 172,411) also discloses using materials manufactured in accordance with this method as contact material for vacuum contactors and teaches incorporating in these materials additions of at least one of the metals, tellurium, antimony, bismuth, or tin, as well as their alloys, to reduce the welding load. The introduction of the additives into the contact pieces fabricated according to the previously known method takes place by subsequent alloying in or diffusing in. However, this is comparatively cumbersome and expensive.
Tellurium, selenium, antimony, and bismuth have all proven to be suitable addition components for copper-chromium contact materials for welding load reduction. The above-mentioned elements are, however, characterized by a high vapor pressure so that additions of these elements evaporate readily in arc melting methods. It has also been previously shown that the direct alloying in of these elemental additions in the arc melting of copper-chromium is not possible since these additions evaporate under the influence of the arc due to their high vapor pressure. This leads to the formation of pores in the melt block. This is particularly true if the elemental additions are mixed in the electrode as fine-particled powder. Tellurium, selenium, or antimony form, in combination with cooper, intermetallic compounds which have a reduced vapor pressure and, accordingly, a reduced tendency to evaporate when compared to the components tellurium, selenium, or antimony used in isolation.
However, pore formation also occurs if the elemental additions are not mixed in as elementary tellurium, selenium, or antimony but are instead mixed in as the intermetallic compounds Cu.sub.2 Te, Cu.sub.2 Se, or Cu.sub.3 Sb in a powder form. The discovery of this phenomenon can be traced back to the charging of fine-particled Cu.sub.2 Te or Cu.sub.2 Se or Cu.sub.3 Sb powder with gas. To this day, however, a fine-particled powder is considered absolutely essential for a homogeneous distribution.
Since tellurium, selenium, antimony, or their intermetallic Cu compounds cannot be directly alloyed in as described above during the melt process, tellurium as discussed in Eur. Pat. No. 172,411, has traditionally been introduced following the arc melting and possibly after the corresponding shaping of the CuCr block through, for example, extrusion in a separate finishing step. In this process an additional method step is required which thereby increases the cost of the manufacturing method.